Field of the Invention
The present invention relates to a press machine and a method of controlling the press machine, particularly to an electric servo press and a method of controlling the electric servo press.
Background Information
An electric servo press as a type of press machine includes a servo motor, a power conversion mechanism, a slide and so forth. The power conversion mechanism is configured to convert the rotational driving power of the servo motor into the up-and-down reciprocating motion of the slide. Then, stamping of a workpiece is performed between an upper die and a lower die by the reciprocating motion of the slide.
In such an electric servo press, as described in Japan Laid-open Patent Application Publication No. 2004-058152, for instance, an operator is allowed to set beforehand target speeds for respective virtual rotational angles associated with slide positions. With such setting being done, the operator is capable of setting an optimal production speed.
In this regard, the electric servo press is more flexible than a well-known mechanical press machine using a flywheel. However, in some settings, a high load could act on the servo motor. When the press machine continues to be operated with such a setting being employed, a servo amplifier is inevitably overheated. This results in abnormal stop of the press machine.
In view of the above, as shown in Japan Laid-open Patent Application Publication No. 2004-017122, a technology has been developed that during an automatic operation, the cumulative amount of heat is calculated on the basis of past actually measured values including motor load current, and the slide is configured to be temporarily stopped when either the motor load current or the cumulative amount of heat exceeds a predetermined threshold.